U.S. Pat. No. 5,705,887 has disclosed a low-pressure discharge lamp of this type. At the end of the service life of the low-pressure discharge lamp, when the filament breaks or the emitter material has been consumed, the lamp switches over to cold-cathode operation, which leads to an increase in the cathode fall voltage and therefore to considerable heating of the metal parts in the lamp. The considerable increase in the temperature of the metal parts leads to the metal hydride in the paste which is arranged in the area of radiation from the filament and in contact with the supply conductors on the glass bead breaking down. The decomposition of the metal hydride, in particular titanium hydride, leads to hydrogen being released and the discharge being extinguished on account of the increasing operating voltage of the lamp.
Arranging the paste which contains metal hydride in the region of the radiation from the filament and in thermal contact with the supply conductors leads to reliable release of the hydrogen and therefore to the lamp being extinguished at the end of its service life. However, it has been found that a design of this type can lead to premature failure of the low-pressure discharge lamp if it is operated at a ballast which allows the filament heating current to rise during the preheating phase until the lamp has ignited. In this case, the rise in the filament radiation and the heating of the supply conductors can lead to premature decomposition of the metal hydride. Then, the hydrogen released extinguishes the lamp before it reaches the end of its service life as a result of emitter consumption.